Abstract

The low-temperature electronic spectra of at an octahedral site of symmetry in the moiety, in crystals of and have been measured and interpreted. Together with the results from emission spectra and resonance electronic Raman spectra, these new data permitted the assignment of symmetry representations of up to 39 out the possible 40 crystal field levels of the configuration. The inclusion of configuration interaction with the next highest even parity configuration, into the energy level parametrization reduced the mean deviation of the energy level fit using the single configuration model alone, by a factor of 2.9 (i.e., from 32.7 to 11.6 cm−1). In particular, the interaction mechanism for the “anomalous” multiplets and was shown to arise from crystal field mixing with states. This leads to the inclusion of up to about 0.5% of fp-orbital character for these eigenvectors. In the single-configuration fits to triplet levels alone, the fourth-degree crystal field parameter turned out to be larger than in the fits to singlet terms, which is the reverse of the expected order if correlation crystal field effects are important.